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Celebrity trainer David Kirsch is known for lifting, firming, and toning some of the best bodies that appear on the runway, silver screen, and glossy magazine covers. Heidi Klum's flat stomach? Kirsch-ed. Karolina Kurkova's lifted tush? Kirsch-ed. Liv Tyler's everything? Kirsch-ed. The latest addition to the Manhattan-based, nutrition-obsessed trainer's collection of toned clients is none other than Kate Upton, two-time cover girl of the Sports Illustrated swimsuit issue and owner of the most enviable set of boobs we've seen, ever. The two first started working together in August out of Kirsch's Madison Square Club when she wanted some basic body maintenance, and things went into overdrive once it started to get closer to the arctic photo shoot. "I made it very clear to her, I love her curves and I wasn't going to do anything to [make her] skinnier," said the body-conscious Kirsch. "It was about toning her legs, butt, abs, arms, and to really dial into the diet."

Which of her body parts did you try to focus on and how?Her abs, butt, legs, thighs, and arms. We did a lot of boxing, kick boxing, and stability ball work. We also did a lot of interval training, like wind sprints on the treadmill and outside. She wasn't a huge fan of those, but it helps to get the overall body toned and it gets the metabolism up.

How often did you two work out together?When she was in New York, I saw her every day, double sessions. She even did extra cardio on her own after the actual workout. It ended up being two to two and a half hours a day for four weeks. That's a lot of Kirsch-ing.

How did you change her diet and nutrition?When we started in August, she started out with the 48 Hour Super Charged cleanse, then moved onto the 5 Day Ultimate Detox. Leading up to the shoot in December, she did the 7 Day Cleanse a couple of times, consecutively.

How did you ensure she didn't lose too much of the curviness for which she's famous?Look, she's eating [well], she's cleaned out of the junk, but ultimately it's genetics. She's got curves. There was no way I was going to "uncurve" her. That was never my objective. I didn't do a lot of weights with her. Instead we did a lot of floor movements and working out with resistance bands. At the end of the day, the objective was not to look like a runway model, but tighten up what she's got to look as amazing as she can.

Are you happy with how she looks in Sports Illustrated?Have you seen the body paint pictures? They're great. The cover? I don't think they used the best picture. I don't know how they ultimately determined that. Maybe they just wanted to show a lot of boob and I guess that's because of their target audience.

What's your favorite aspect of her body?I love curves. She is the quintessential all-American girl. She's fresh, sunny, and natural, and not too skinny. We're not advocating that stick-thin, unhealthy, anorexic approach to modeling. She's got a little extra meat. I love that physical aspect of her from her chest to curvy hip. I saw a great difference in her core from before we started to when she shot with SI. Her butt, thighs, and legs got stronger, leaner. It was from all those dead lifts, sumo lunges, and platypus walks. All of those exercises are about tightening and toning.

What's your take on the haters out there who think she's too curvy?I posted all of her pictures from SI on my Facebook and there were the people who said, "Oh she's porky, she's fat." But my response is, "You guys are all entitled to your opinion, and I know I'm biased, but I would sooner have that healthy body than one that is too thin." She also embraces it. She's like, "I got great boobs. Hello, they're there. They're not going anywhere."

So speaking of those boobs, how many sports bras did she have to wear to rein those in?No comment, no comment. [Though lots of laughing.]

The Superman and swimming exercises are good for back workouts. Lay on your stomach and lift opposite arm to opposite leg for about 30 sec. You can also lift both arms and legs and move them in a swimming motion. Try to lift your chest of the ground and make sure your spine's aligned to prevent injury.

my mom + her friend were all about the green coffee bean extract for a while, though i really couldn't tell you what happened to their craze. i'm assuming it didn't work for them because it faded away and now i never hear about it.